Electrical probes for neural stimulation have been in existence for some time. The study of optogenetics requires illumination of selected areas of treated tissue with light of a specific wavelength and the ability to record the responses of neuron activity in the area. Probes have been developed which allow illumination of an area of tissue by the incorporation of an optical fibre waveguide or an integrated waveguide.
Prior uses of optogenetics have been demonstrated using optical fibres illuminated from a remote source. The remote source typically used is either a relatively expensive laser or a macro LED, the latter having a low optical coupling efficiency, such that only a small fraction of the light is delivered to the fibre. The light emitted from optical fibres is neither collimated nor focussed but, as the numerical aperture of the fibres is typically quite low the light output required (power density) to elicit a response is modest. This has some advantages but the construction of these hybrid probes is prohibitively expensive. Additionally, the spacing between the light source and receptors is not controlled. Typically, only one fibre from an external light source is available on each hybrid probe as the shank width is too small to accommodate multiple fibres. This restricts the emission to one wavelength at any given time, making simultaneous stimulation and inhibition difficult. The fibre is typically placed far away from the probe distal end and light is directed in the direction of the distal end where the sensors are placed so that there is illumination across the detector elements. Consequently, this leads to non-uniform illumination at varying sensor positions (absorption and scattering of the incident light) and optical artifacts caused by the incident light shining on the detector. A possible mechanism to improve this is to etch a hole in the Si probe and placement of the fibre inserted in a trench on the probe backside with a 45° angled facet so that the light is directed out of the plane of the probe. However, this is prohibitively expensive and only very skilled labour would be in a position to fabricate such a structure.
In US 2011/0087311 there is a microstructure probe for delivering light of variable colour and/or power, via a set of integrated light guides, from a source (or set of sources) to regions spatially arranged 3-dimensionally, with a length scale of microns to millimeters. In exemplary embodiments of this invention, a microstructure probe comprises many lightguides and is adapted to be inserted into neural or other tissue. The lightguides run in parallel along at least a portion of the axis of the probe. US 2011/0087311 is incorporated herein by reference.
Most optogenetics activate or silence large populations of a given cell type or pathway. It is therefore a preferred feature of the present invention to provide a neural probe which will enable improved resolution of location between emitter to emitter and emitter to sensor and sensor array. This will greatly increase the power of optogenetics to understand neural activity patterns in brain functions.
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide an improved neural probe.
It is a further object of at least one aspect of the present invention to provide a method of manufacturing an improved neural probe.